linux-kernel - Re: drivers/char/random.c line 728 BUG

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Message-Id: <20080829125445.9e48b1f1.akpm@linux-foundation.org>
Date:	Fri, 29 Aug 2008 12:54:45 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	aaron@...finllc.com, mpm@...enic.com, linux-kernel@...r.kernel.org,
	tytso@....edu, stable@...nel.org
Subject: Re: drivers/char/random.c line 728 BUG

On Fri, 29 Aug 2008 12:48:07 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> We could fix this by moving the assertion inside the lock, but it seems
> safer and saner to revert to the old behaviour wherein
> entropy_store.entropy_count at no time exceeds
> entropy_store.poolinfo->POOLBITS.

The fixed version even generates improved code.

Let's try to avoid repeats:

--- a/drivers/char/random.c~drivers-char-randomc-fix-a-race-which-can-lead-to-a-bogus-bug-fix
+++ a/drivers/char/random.c
@@ -407,7 +407,7 @@ struct entropy_store {
 	/* read-write data: */
 	spinlock_t lock;
 	unsigned add_ptr;
-	int entropy_count;
+	int entropy_count;	/* Must at no time exceed ->POOLBITS! */
 	int input_rotate;
 };
 
_

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